Neptune Facts

Neptune is the eigth and the last planet in the solar system. This cold and dark planet ravaged by winds is the third-most massive planet and fourth-largest by diameter in the solar system. Neptune shares many of its characteristic with its twin Uranus.

Neptune Profile

Interesting Neptune Facts

  • Neptune is the eighth and the farthest planet from the sun since Pluto was declared a dwarf planet.
  • It is around 4.5 billion km that is nearly 30 astronomical units away from the sun.
  • Neptune is so far away that the light of the sun takes around 4 hours and 12 minutes to reach the Neptune.
  • It is the fourth-largest planet and the third most massive planet in the solar system.
  • It is the densest of the giant planets in the solar system.
  • The period of rotation of the planet is 16 hours and 6 minutes.
  • Neptune is known to have 14 moons.
  • Only one spacecraft that is Voyager 2 by NASA has flown by Neptune.
  • Neptune is known to have several faint rings around it.
  • Neptune magnetic field is about 27 times stronger than that of the earth.
  • Neptune shows variations just like the Earth or Uranus magnetic field.
  • It is not impossible for life to exist on Neptune.
  • Although Pluto is farther away from the sun than Neptune, it is sometimes closer to the sun than Neptune because of the nature of their orbits.


Neptune was formed around 4.5 billion years ago. It is one of the very few celestial bodies that was not known to the Ancients because of its large distance from the Earth. Galileo Galilei made the first observations regarding the different positions of the planet in 1612 and 1613 but he assumed it to be a star in the night sky.

Hence, he is not credited for the discovery of the planet. The astronomical observations about the planet were given by Alexis Bouvard in 1821. Several astronomers tried to observe and record information regarding Neptune’s orbit in the subsequent years using telescopes and data about Uranus.

Neptune’s Discovery

Most important contributions regarding the planet were put forward by Urbain Le Verrier and John Couch Adams. Soon, Neptune was identified as a planet. There was an argument between the British and the French about who should get the credit for the discovery of the planet.

It was then concluded that both the astronomers should be credited as a ‘co-discovery’.  After being officially discovered, Neptune was often referred to as ‘Le Verrier’s planet‘ or ‘the planet exterior to Uranus’.


The name Neptune was put forward by Le Verrier. In Roman mythology, Neptune is the god of the sea. In Greek mythology, the same god is called Poseidon. The planet was named after a mythological figure to keep with the nomenclature of all the other planets which were also named after figures from Roman and Greek mythology, besides the Earth.

The name is also appropriate because of the blue appearance of the planet. Until the discovery of Pluto in 1930 Neptune was the farthest known object in the solar system. Neptune was thus considered the farthest planet from the sun until Pluto was declared as a dwarf planet in 2006


Neptune has a striking blue color which is quite different from that of all the other planets. Just like Jupiter has a great red spot, Neptune is known to have a great blue spot. It is believed that the spot can fit an entire Earth inside it. Thick white clouds are often seen around the planet.

Neptune also has a few smaller spots that come and go. The spots are Storms going on the planet. Since it is so far away from the Earth, Neptune cannot be seen with the naked eye. Like Jupiter, Saturn, and Uranus Neptune also has rings.

These rings are very faint and some of them are incomplete. Some of them also appear to be twisted. The rings of Neptune are still a mystery to human beings. However, it is known that there are five primary rings around the planet.

Methane present in the atmosphere absorbs the red light and gives out the blue light making the planet appear the way it does. However, Uranus also has an abundance of Methane and its atmosphere doesn’t have the blue color as that of Neptune.

This means that there is a possibility of another unknown substance being present in Neptune’s atmosphere. The appearance helps distinguish the planet from Uranus.


Neptune is 4.5 million km away from the Sun.  It is the fourth-largest planet in terms of size and the third-largest planet in terms of mass. It is the smallest of all the gas planets.


Being a gas giant Neptune does not have a definite surface. Just like Uranus, Neptune is also considered as an ice giant. The internal structure of the planet is quite similar to that of Uranus. It has an upper layer where it has an atmosphere which is full of clouds.


It has a mantle mostly consisting of water, ammonia, and methane. It has a core that consists of rocks of iron, nickel and some silicates. The core acts as an internal heat source that radiates about twice the energy that it receives from the Sun. Neptune’s core is a little larger than that of planet Earth.

Magnetic field & Gravitational Forces

Neptune’s magnetic field axis is tilted at about 47° which is similar to Uranus’ axis which is tilted at 60°. Hence just like Uranus, Neptune shows drastic variations in its magnetic field. Neptune magnetic field is about 26 times stronger than that of the earth. Neptune has a much hotter core, which is around 7,000°C.

Orbit & Rotation

Neptune takes nearly 165 years to complete one revolution around the sun.

The planet takes 16 hours and 6 minutes to rotate about its axis. The equatorial radius of the planet is nearly 24800 km. Neptune is 17 times larger than the earth.


Neptune has a very thick atmosphere. About three quarters that is 75% of the atmosphere consists of hydrogen and the remaining consists of helium and methane.

Neptune’s atmosphere is divided into two parts. The first is the lower troposphere. In this layer the temperature decreases as we go up. The second layer is the stratosphere where temperature increases with altitude, contrary to the first layer.

Before stratosphere come the small layers of the thermosphere and finally the exosphere. The thermosphere is known to have traces of carbon dioxide and water. The presence of Methane and other gases in the extremities gives Neptune its striking blue appearance.


Neptune is known to have 14 moons all of which are named after characters from Greek mythology. The largest moon of the planet is Triton which was discovered by William Lasswell in 1846, only a few days after the discovery of the planet itself.

Triton consists of most of the mass of the Neptunian Moon system. The second moon, Nereid was discovered almost a hundred years after the first one. The third of Neptune’s moons to be discovered was Larissa. It was discovered in 1981.

In 1989, NASA’s Voyager 2 discovered 5 more moons, namely, Naiad, Thalassa, Despina, Galatea, and Proteus. In 2001, 5 more moons were discovered. These were Halimede, Sao, Psamathe, Laomedeia, and Neso. This brought the total to 13 moons.

In 2002 another moon was sighted but was soon lost. So, it may have been a centaur or a comet. However, the size, dimensions, and motion of the moon relative to the planet confirmed that it was a satellite, bringing the total to 14 moons. This moon is called Neptune XIV.

Neptune XIV has not yet been officially confirmed. Neso is Neptune’s outermost moon. Distance between Neptune and Neso is the largest between any planet and its moon in the solar system.

The moons of Neptune are divided into two groups, regular and irregular. All the 7 inner moons are regular moons. All the other moons, including Triton, fall into the second group. Proteus is the largest of the inner moon and the second largest of all the other moons of Neptune. 


Winds on Neptune

Neptune has very strong and fast winds, the speed of which can sometimes reach up to 700 miles an hour. Winds on Neptune are three times stronger than those on Jupiter which are 9 times stronger than those on earth.

Rings of Neptune

Neptune is known to have several faint rings around it. This Ring is thought to be relatively younger. The Neptunian ring system primarily consists of five main rings. They were first discovered in 1984 by Patrice Bouchet, Jean Manfroid and Reinhold Häfner. The Neptunian ring system is dusty, faint and not easily visible.

They are almost as dense as the ring of Saturn’s ring system. The rings of Neptune are believed to be made up of dark organic matter. Some of these rings are irregular and even incomplete.

In order of increasing distance from the planet, these rings are named Galle, Le Verrier, Lassell, Arago and Adams. They are named after the astronomers who made significant contributions towards the study of Neptune.

Three rings of Neptune are about 100 km in width while two rings that is the Galle and Lassell rings are quite broad with a width of nearly 2000 to 5000 km.

Many of Neptune’s moons have orbits inside of this ring system. These rings are very different from those of Saturn and Uranus but similar to those of Jupiter. Not much is known about these rings.


Galileo Galilei became the first person to observe Neptune through a telescope in 1612.  Subsequently, Neptune was extensively observed but only through telescopes. The first spacecraft to visit Neptune was launched in 1977 by NASA which also visited Jupiter, Saturn, and Uranus.

Another spacecraft called Pioneer 10, on the way to Aldebaran i.e. the red star crossed the orbit of Neptune in 1983. Neptune has only been visited by one spacecraft that is Voyager 2 by NASA in 1989. Voyager 2 is also the only spacecraft to have visited Uranus.

Neptune is so far away from the Earth that it took the spacecraft almost 12 years to reach the planet.  It made its closest approach to the planet on 25th August 1989. It went as close as 5000 km above Neptune’s the North Pole.

It studied Neptune’s atmosphere, rings, moons, and magnetosphere. The spacecraft revealed that the great white spot of the planet was similar to Jupiter’s Great Red Spot. Voyager 2 discovered 6 new moons of Neptune and clicked photographs of three of them.

The spacecraft provided great details about the planet. The only other means of observing Neptune are some powerful telescopes on Earth like the Hubble Space Telescope. Several missions like spacecraft, flybys or probes to be sent to Neptune have been proposed but none of them have been approved yet. 

Potential for Life in Neptune

No evidence of life has ever been found in Neptune. It is believed that life has never existed on the planet and it is not possible for life to thrive on the planet in the future either. The conditions on Neptune like temperature, pressure, wind speeds, etc. are too extreme for any living organisms to sustain.

However, water exists in the interior of Neptune. This means that it is not impossible that life may exist on the planet. It will, however, be a very different kind of life than that found on the Earth. To know more about this, the planet would be needed to be studied in great detail which is a little difficult in today’s technology as the atmosphere of Neptune will not be friendly for a spacecraft. Hence, facts about this are still a mystery to us.

Neptune in Pop Culture

Despite its great distance from the Sun, Neptune has found a place in pop culture on the earth. Event Horizon, a science fiction horror film of 1997 used Neptune as its backdrop. It has found significant mentions in Futurama, the Dr. Who episode called ‘Sleep No More’ and in an episode of Star Trek. 


  • 1846: Neptune is collectively discovered by Johann Gottfried Galle, Urbain Le Verrier, and John Couch Adams
  • 1846: Neptune’s moon Triton is discovered
  • 1983: Pioneer 10 crosses the orbit of Neptune
  • 1989: 3 of Neptune’s moons are discovered
  • 1989: Voyager 2 passes within 3000 miles of Neptune, sends back 3 photographs
  • 1989-present: Efforts to study Neptune more deeply continue